题目链接：https://vjudge.net/problem/HDU-1285

邻接矩阵存储版

#include<iostream>
#include<queue>
#include<cstring>
#include<functional>
#include<vector>
using namespace std;
const int N = 510;
int n, m;int g[N][N], in[N]; // in[i]记录i的入度数   g为邻接矩阵void solve() {priority_queue<int, vector<int>, greater<int> > q;  // 使用小根堆（题目要求：符合条件的排名可能不是唯一的，此时要求输出时编号小的队伍在前）vector<int> ans;memset(g, 0, sizeof g);memset(in, 0, sizeof in);for (int i = 0; i < m; i ++) {int a, b;cin >> a >> b;if (g[a][b]) continue; // 用邻接矩阵注意重复边 g[a][b] = 1;in[b] ++;}for (int i = 1; i <= n; i ++)if (in[i] == 0) {q.push(i);while(!q.empty()) {int t = q.top();q.pop();ans.emplace_back(t);for (int i = 1; i <= n; i ++) {if (g[t][i] == 1) {in[i] --;if (in[i] == 0)q.push(i);}}}for (int i = 0; i < ans.size(); i ++) {if (i == 0) cout << ans[i];else cout << " " << ans[i];}cout << endl;
}int main() {while(cin >> n >> m) {solve();}return 0;
}

邻接表版

#include <iostream>
#include <vector>
#include <queue>using namespace std;int main() {int n, m;while(cin >> n >> m) {vector<vector<int> > g(n + 1);vector<int> indegree(n + 1);// 符合条件的排名可能不是唯一的，此时要求输出时编号小的队伍在前priority_queue<int, vector<int>, greater<int> > heap; // 小顶堆// 初始图，并统计入度for (int i = 0; i < m; i ++) {int a, b;cin >> a >> b;g[a].push_back(b);indegree[b] ++;}// 将入度为零的加入小顶堆for (int i = 1; i <= n; i ++) if(indegree[i] == 0) heap.push(i);vector<int> ans; // ans 用于收集结果 while(!heap.empty()) {int t = heap.top();heap.pop();ans.emplace_back(t);// 更新入度数组 ，入度为零则加入队列 for (int i = 0; i < g[t].size(); i ++) { indegree[g[t][i]] --;if (indegree[g[t][i]] == 0) {heap.push(g[t][i]);}}}for (int i = 0; i < ans.size(); i ++) {if (i == 0) cout << ans[i];else cout << " " << ans[i];}cout << endl;}return 0;
}

链式前向星版

#include<iostream>
#include<queue>
#include<cstring>
using namespace std;
const int N = 550;
const int M = 2.5e5;
int n, m, idx;
int indegree[N];
int head[N];
struct edge {int to, next;
};
edge e[M];
void add(int a, int b) {e[idx].to = b;e[idx].next = head[a];head[a] = idx;idx++;
}
void init() {idx = 0;fill(head, head + N, -1);
}void solve() {priority_queue<int, vector<int>, greater<int> > q;vector<int> ans;init();memset(indegree, 0, sizeof indegree);for (int i = 0; i < m; i ++) {int a, b;cin >> a >> b;add(a, b);indegree[b] ++;}for (int i = 1; i <= n; i ++)if (indegree[i] == 0)q.push(i);while(!q.empty()) {int t = q.top();q.pop();ans.emplace_back(t);for (int i = head[t]; ~i; i = e[i].next) {indegree[e[i].to] --;if (indegree[e[i].to] == 0) {q.push(e[i].to);}}}for (int i = 0; i < ans.size(); i ++) {if (i == 0) cout << ans[i];else cout << " " << ans[i];}cout << endl;
}int main() {while(cin >> n >> m) {solve();}return 0;
}